The TechNet Magazine (May-June 2006) included an article:
“Inside Microsoft.com Moving Microsoft Update Downloads to x64”
about why the Microsoft.com (MSCOM) Ops. team moved the Windows Update site to x64.
The MSCOM Ops blog has also posted a response:
“User Mode or Kernel Mode Which Caching Method Did We Use” to the article.
Read the article here at TechNet.